In case I need to remember that I did this...
By default, the Mac Terminal assigns the "Clear Scrollback" command to Command-K. This is annoying, because I often use Nano, which uses Control-K to cut a line of text, and I frequently press Command-K instead of Control-K by accident. This clears my screen while I'm in the middle of editing a file. Very annoying.
The solution is to assign a new (harder to hit by accident) command to the "Clear Scrollback" command, so that when I inevitably mistype Command-K, nothing happens.
